Marked improvement was made on the maturation of megakaryocytes by replacing the NCTC 109 in my culture with the synthetic hormone medium. More small megakaryocytes (megakaryoblasts) were observed. Maturation of cells into promegakaryocytes, granule formation, and demarcation membrane formation were observed regularly in every experiment. The number of neutrophils was also markedly increased. At the end of 10 days, numerous neutrophils, single or in small colonies, were present in the cultures. Furthermore, eosinophils were also observed throughout the period of observations. This is surprising, since growth of these cells requires a specific stimulating factor from the serum of parasite-infected animals. Since maturation of the three important narrow cells were observed in the present liquid culture, this culture could be the first cell model suitable for studies of cell maturation of various types of marrow cells.